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Case Study: GRP Tank Cover - Hoo Green WwTW

  • GRP Tank Cover
  • GRP Tank Cover
  • GRP Tank Cover
  • GRP Tank Cover
  • GRP Tank Cover
  • GRP Tank Cover

Industry Sector

Wastewater Treatment


Hoo Green Wastewater Treatment Works, Knutsford, Cheshire, England


Removable GRP odour control tank cover to encase a wastewater biological disc.


6120 x 3030mm GRP Domed Shaped Self-Supporting Tank Cover.


12 no. 400x500mm lockable hatches.

2 no. air vents with integrated insect screen.

Flanges for fixing to existing plinth.


Relinea were appointed to design and manufacture a Glass Reinforced Plastic (GRP) removable odour control tank cover to mount a wastewater biological disc within Hoo Green Wastewater Treatment Works. The new GRP tank cover was required to replace the existing damaged and corroded cover.


It was essential that the dimensions of the new GRP tank cover matched the existing tank cover in place to ensure that the new cover was within tolerance of the existing plinth since the machinery housed internally had a required clearance. For ease of installation, it was necessary that the tank cover could be easily manually handled by two men.


To ensure that the dimensions of the new GRP tank cover replicated the existing plinth, Relinea’s installation team conducted an onsite measure and subsequently manufactured a mould replicating the existing tank dimensions taken onsite, whilst incorporating an outdoor loading of 0.48 KN/m2.

The GRP tank cover was manufactured using a high chemical resistant resin to protect the cover from the aggressive chemical environment it would be exposed to, and to ensure that the tank cover remained structurally sound and maintenance free.

The tank cover was constructed in 6 no. interconnecting segments using toggle joints to connect each segment together. In order to contain the odour emitting from the wastewater biological disc, neoprene gaskets were placed between each segment to provide a fully functional odour control cover.

Since each tank cover segment required ease of handling by two men, handles were incorporated onto the lightweight GRP cover to aid lifting for a safer and more efficient installation. Finally, inspection hatches were installed onto the moulded tank cover, so that maintenance procedures could be easily carried out by the plant operatives on the internal wastewater biological disc. 

The corrosion resistant characteristics of GRP meant that Relinea’s bespoke odour control tank cover offered the Hoo Green Wastewater Treatment Works a highly durable and low lifecycle cost product. The project was a success and client was very satisfied with the quality and aesthetic appearance of the GRP tank cover.